This invention relates in general to certain new and useful improvements in filter plates of the type used in filter presses, and more particularly, to a filter plate which is constructed of a frame and integral expandable plate forming walls or skins with an interior core capable of being expanded upon the introduction of an expanding fluid therein and which also provides excellent heat transfer characteristics, as well as accessories for such plates.
Liquid-solid separation has, for many years, been an integral part of processes in many industries and primarily the chemical industry where it is often necessary to separate liquids from solids for purposes of reclaiming either the solids or the liquids, or both. Liquid-solid separation is also involved in numerous other industries as, for example, the food industry where the edible food product is oftentimes recovered from a liquid containing slurry, and waste management where it is necessary to dispose of the solid waste material and possibly reclaim or recycle the liquid.
One of the principal-devices for causing liquid-solid separation is a filter press and these filter presses conventionally use a plurality of marginally registered stacked filter plates. Each of the filter plates comprise a plate structure having a filter membrane or so-called "screen" disposed across the plate. The filter plates are held in tight engagement with one another in a stacked arrangement to enable the liquid to be passed through the filter or screen and allowing the solid or solids to form on the screen as a cake.
Numerous filter plate designs are available in the prior art. Each of these filter plates have a main peripheral frame with a central plate structure extending across the frame. A separate filter or screen is placed on each of the sides of the frame. The liquid slurry containing the solid is then pumped through the filter plates and brought into contact with the screens, usually under pressure. The solid material in the slurry forms as a cake on the exterior sides of the screens allowing the liquid to pass through the screens and into a duct network connected to the filter plates and delivered to a collection area.
One of the major drawbacks of the type of filter plates heretofore described is that in the absence of some type of plate expansion, the water extraction process is relatively slow. Thus, separation of liquid from water, depending upon the type of materials involved, can take many hours. This necessarily slows down an entire process or otherwise, requires the provision of a large number of filter presses.
Each of the conventional filter plates usually employ a filter screen having a pair of filter sheets or so-called "screens" with one on each of the opposite sides of the plate. The filter plate is provided with a central feed opening and the screen, which is usually in the form of a fabric gauze material, is stuffed through the hole so that the sheet can open on each of the opposite sides of the plate. However, this construction necessarily limits the plate to a single screen and furthermore, to a single feed duct.
There have also been many commercially available diaphragm plates which are available in the prior art. These diaphragm plates are typically constructed of a relatively rigid frame member, such as a rectangular frame, and have elastomer sheets connected to each of the sides of the frame on the exterior thereof in order to form a type of plate structure. The elastomer sheets are expandable outwardly so that when a fluid is introduced into the plate, a pressure will build up behind the elastomer sheets causing the elastomer sheets to expand.
In the conventional filter press, a pair of plates lie in juxtaposed arrangement with respect to one another and hence, the screens on those plates lie in juxtaposed arrangement. The slurry is introduced into the cavity between the two screens and when the elastomer sheets expand against the slurry captured between two plates this forces a greater separation of the liquid-solid slurry.
These diaphragm plates have several disadvantages. First of all, the diaphragm plate has little heat transfer capability. Consequently, it is difficult, if not virtually impossible, to control the temperature of the slurry which may be desirable, if not absolutely necessary in many chemical process operations. Equally disadvantageous is the fact that the elastomer membrane is secured within a groove formed in the interior of the frame.
However, this structure is not capable of withstanding any significant pressure if the diaphragm plate is inadvertently expanded when not in the confines of a press. Consequently, the elastomer will literally blow out of the frame itself, thereby totally destroying the frame.
If several frames are located in a press and adequate pressure is not applied to the frames before an expansion process begins, then several plates could all simultaneously be destroyed. These plates are quite expensive and therefore, destruction of the plates can be cost prohibitive and materially add to the overall cost of the process.
There has been a need. for a filter plate which provides excellent heat transfer characteristics and does not suffer the problems of a potentially rupturing diaphragm and which still maintains excellent structural integrity with expansion characteristics. There has also been a need for a filter plate having a screen which can be easily replaced and which can be readily reused.